1. Field of the Invention
This invention relates to rotary machines, and more particularly to rotary seals between the rotating and stationary components of the machine.
2. Description of the Prior Art
Rotary seals such as a labyrinth seal are typically utilized with rotating machinery to impede the leakage of a medium between rotating and stationary components from a high pressure region to a low pressure region. A labyrinth seal is formed of a sealing surface on one component and a restrictive ring on the other component which projects into close proximity with the sealing surface. A plurality of restrictive rings are commonly disposed in series to form alternating flow throttling and expanding regions along the labyrinth seal to reduce the pressure of the leakage medium through the dissipation of kinetic energy.
In gas turbine engines labyrinth seals are typically used to prevent the excessive leakage of air into the bearing compartments and to prevent the excessive leakage of air externally of the working medium flow path from one engine stage to another. One construction for sealing between adjacent stages in the turbine section of an engine is shown in U.S. Pat. No. 3,514,112 to Pettengill entitled "Reduced Clearance Seal Construction". A plurality of restrictive rings in Pettengill project toward corresponding sealing surfaces. A throttle aperture is formed between each ring and its corresponding sealing surface. An expansion chamber is formed between each pair of adjacent rings. Air leakage through the first throttle aperture flows through the downstream chambers and apertures to establish a stable pressure differential across the labyrinth.
In U.S. Pat. No. 3,572,728 to Smuland entitled "Rotary Seal", means disposed immediately downstream of the restrictive ring reverses leakage fluid back upstream toward the throttle aperture to decrease the apparent pressure differential across the aperture. The Smuland seal is effective in constructions having a small clearance between the restrictive ring and the sealing surface. Under large clearance conditions the leakage fluid tends to stagnate in the reversing region and the functional ability of the means becomes reduced.
In gas turbine engines diverse thermal environments frequently necessitate substantial initial clearance between rotating and stationary components to prevent destructive interference under transient conditions. Continuing efforts are underway to discover and develop sealing means between rotating and stationary components which are effective over varied clearance ranges.